1. Field of the Invention
This invention relates to an electrical circuit protection device, and in particular, it relates to a ground-fault circuit interrupter (GFCI) device for disconnecting an input side and an output side of an electrical circuit.
2. Description of the Related Art
To prevent harm caused by leakage current in home appliances, such as water heaters and refrigerators, it is common to use a ground-fault circuit interrupter (GFCI) device for the power input of the appliances, such as by employing a power receptacle having a leakage current protection function.
Currently, most GFCI devices have leakage current protection functions, but require manual testing (e.g. a user manually depressing a test button) to test whether the protection function of device is working properly. If the user does not periodically test the device manually, and the GFCI device malfunctions due to internal problems and fails to disconnect the input and output sides, accidents such as electric shock or fire may occur.
Some GFCI devices have a self-test function to detect whether the protection function of the device is working properly. Such a device periodically outputs a self-test signal to generate a simulated ground fault current on the hot conductor of the device. The device detects whether a self-test feedback signal is generated in order to determine whether the protection function is working properly.
For example, in China patent application CN 200510083979.4, a self-test signal is generated near the 140 to 150-degree position of the sine wave (i.e. in the dropping part of the positive half-cycle) of the power source. Because the anode and cathode of the silicon-controlled rectifier (SCR) will automatically become non-conducting when the power source signal passes zero points, this self-test method may adversely affect the normal detection of ground faults, and may cause the GFCI device to trip erroneously.
In other examples, such as U.S. Pat. No. 7,443,309, U.S. Pat. Appl. Pub. No. 20090251148, and China patent application CN 200610007854.8, the SCR of the GFCI is conductive during the positive half-cycle of the power source, and the device uses the negative half-cycle of the power source to generate self-test signals to perform self-test. This method does not cause erroneous tripping; however, if a ground fault occurs during the self-test period, the simulated ground fault current caused by the self-test signal is superimposed on the true ground fault current, adversely affecting the detection of the ground fault current in the negative half-cycle. Further, because the SCR is not conductive in the negative half-cycle, the reaction time of the GFCI device is increased for those ground fault conditions that start in the negative half-cycle of the power source.